Wall shear stress measured by phase contrast cardiovascular magnetic resonance in children and adolescents with pulmonary arterial hypertension

Abstract

Background: Pulmonary arterial hypertension (PAH) is a devastating disease with significant morbidity and mortality. At the macroscopic level, disease progression is observed as a complex interplay between mean pulmonary artery pressure, pulmonary vascular resistance, pulmonary vascular stiffness, arterial size, and flow. Wall shear stress (WSS) is known to mediate or be dependent on a number of these factors. Given that WSS is known to promote architectural vessel remodeling, it is imperative that the changes of this factor be quantified in the presence of PAH.

Methods: In this study, we analyzed phase contrast imaging of the right pulmonary artery derived from cardiovascular magnetic resonance to quantify the local, temporal and circumferentially averaged WSS of a PAH population and a pediatric control population. In addition, information about flow and relative area change were derived.

Results: Although the normotensive and PAH shear waveform exhibited a WSS profile which is uniform in magnitude and direction along the vessel circumference at systole, time-averaged WSS (2.2 ± 1.6 vs. 6.6 ± 3.4 dynes/cm(2), P = 0.018) and systolic WSS (8.2 ± 5.0 v. 20.0 ± 9.1 dynes/cm(2), P = 0.018) was significantly depressed in the PAH population as compared to the controls. BSA-indexed PA diameter was significantly larger in the PAH population (1.5 ± 0.4 vs. 0.7 ± 0.1 cm/m(2), P = 0.003).

Conclusions: In the presence of preserved flow rates through a large PAH pulmonary artery, WSS is significantly decreased. This may have implications for proximal pulmonary artery remodeling and cellular function in the progression of PAH.

Figure 1

Phase-contrast imaging through the right pulmonary artery. Segmented (a) intensity and (b) phase contrast images (RPA lumen shown in green).

Figure 2

RPA area change and relative size. Normotensive (a) and PAH subjects (b) are shown with the calculated diameter (D), as back-calculated from diastolic cross-sectional area.

Figure 3

Regional wall shear stress in systole in the normotensive population (n = 4) compared to the PAH population (n = 25). P < 0.05 is indicated by ‘*’.

Figure 4

PAH patient morphology and WSS summary. Morphology, velocity, flow, and WSS summary for (a) an example normotensive subject and (b) an example PAH patient. The subjects are and BSA matched. Note the drastic overall WSS reduction in the PAH patient.

Figure 5

Cross-sectional average of WSS_systole in PAH patients as compared to normotensive controls (‘*’ indicates P < 0.05). P < 0.05 is indicated by ‘*’.

Figure 6

Relationship between right pulmonary arterial diameter and WSS with BSA in controls and subjects with pulmonary arterial hypertension. (a) RPA diameter and WSS measurements in systole demonstrate a BSA dependence in both cohorts. The white line indicates the regression model (y = ax^0.5) for the control group, with the blue shaded region indicating the 95% confidence region; the dashed line indicates results (n = 496) from Sluysman et al. [26]. (b) WSS decreases rapidly as a function of the BSA-indexed RPA diameter. Solid markers indicate subjects with cross-sectional profiles plotted in Figure 2. The regression line in (b) is an inverse cubic regression, reflecting the inverse proportional relationship between WSS and the vessel radius cubed. Note: diameter measurements are augmented with data collected in previous echo-based studies [33]; WSS measurements are from CMR-only.